The steering of tracklaying vehicles or wheeled vehicles with wheel-side steering is known in that a steering movement is superimposed on the actual traveling movement to the effect that the driving speed is increased on outside curves and is reduced on inside curves. The actual drive system can thereby be graduated or continuous. The superposition of the steering movement takes place via summing gears, which are primarily located directly on the two gear driven ends. The summing gears are usually connected via a mechanical shaft-the so-called zero shaft-which makes possible a power flow from the inside curve to be braked to the accelerating outside curve and keeps the steering power required by the drive motor low.
The drive of the zero shaft or the steering system takes place in generally known embodiment variants in that power is branched off from the actual traction motor and is transferred to the zero shaft via continuous hydrostatic drives or via power-branched, continuous hydrostatic, mechanical or continuously hydrostatic-hydrodynamic drives.
What all mechanical and hydrostatic arrangement variants have in common, whether combined with hydrodynamics or not, is that the steering actuation is carried out in a single circuit; that is, with a breakdown of the hydrostatics, above all, with a breakdown of the mechanical-hydraulic steering of the hydrostatics, the steering system fails. The provision of a dual circuit—that is, two parallel steering actuations-leads in principle to greater complexity and further increases the risk of breakdown, since, for example, additional couplings must be incorporated, that must turn off the branch which is emitting a false steering signal.
From DE 37 28 171 C2, a continuous drive assembly for a steering system by means of an electric motor is known. This purely electrical steering system can be carried out with a dual circuit since the circuit that receives the false steering can be electrically monitored and switched off. The defective electric motor can be idled in this case, by the still intact electric motor.
Electrical steering systems, however, require, together with the needed power circuitry, an essentially larger structural space than mechanical, hydrostatic, or hydrodynamic assemblies or corresponding individual solutions.